Seed planters generally include meters of various designs have been used for sometime to dispense seeds at a controlled rate into a seed furrow as the seed meter is advanced above and along the seed furrow. In a typical arrangement, a tractor is coupled to tow a tool bar to which are attached in a generally parallel, spaced apart relation a plurality of planting units with seed meter arrangement attached thereto. Each planting unit typically includes a seed hopper for containing and carrying a large quantity of seeds to be planted or a smaller container fed from a centralized in or large hopper, a device for opening a furrow in the ground as the tractor drawn tool bar is advanced across the field over the ground, a seed meter is coupled to the seed hopper for dispensing individual seeds into the furrow at a controlled rate, and a further device for moving soil at the sides of the furrow to close the furrow over the seeds.
During a planting operation, the tractor typically moves across the field at speeds of about 4 to about 8 miles per hour. The spacing between adjacent individual seeds in each furrow can be as little as 0.5 inches or less or as much as 10 inches or more depending upon the particular seed being planted. The seed metering mechanism therefor must be capable of dispensing seeds at various rates in the order of to 130 seeds per second or greater as well as at rates which are considerably less. The many different types of seeds to be planted using a seed metering mechanism include corn, cotton, sorghum, sugar beets, soybeans and sunflowers to name a few. As will be appreciated, such seeds vary considerably in size, weight and shape. For example, peanut and edible bean seeds are among the largest seeds for planting and have elongated irregular shapes and outer surfaces. Soybean, and pelletized seeds are smaller and tend to be rounder and vary in shape and size. Sorghum and raw sugar beet seeds have a rounder almost spherical appearance. Sorghum seeds have a relatively smooth outer surface. On the other hand, raw sugar beet seeds have a very rough and irregular outer surface configuration. Cotton seed is small and shaped like some corn seed. On the other hand, corn seeds have a somewhat triangular shape with generally flat sides.
Despite these numerous differences in the size, shape and surfaces of such seeds, seed meters are expected and are required to handle all different types of seeds described above plus many more while requiring minimum effort regarding part changes and adjustments. At the same time, required spacing and depth standards of planting accuracy typically mandate a low error rate. A missed seed or doubling of seeds is undesirable and may be tolerated only very infrequently. Such requirements place considerable demands upon the accuracy of the seed metering mechanisms.
Some seed metering mechanisms used in planting operations of the type discussed above are of the mechanical type and include a vertical or horizontal seed plate or disc with mechanically actuated fingers or similarly operated mechanical devices for separating individual seeds from the seed disc and then dispense them into the furrow. While some mechanical seed meters are satisfactory for certain applications, they typically suffer from a number of limitations including the limited speed at which they can accurately dispense seeds, and inability to handle different type seeds without making cumbersome and extensive part changes, and an inherent design complexity which may typically add to the cost, wear and maintenance problems of the mechanically operated seed dispensing mechanisms.
Alternatively, a seed metering mechanism which utilizes an air pressure differential has been developed in an effort to overcome some of the problems of the mechanical seed meters. Air pressure differential seed meters, which are commonly known as air seed meters, are generally of two types. The first type being the positive pressure type and the second type relying upon negative pressure or vacuum.
In the positive pressure type of air seed metering mechanism, air is blown into the seed chamber and onto the surface of a rotating or otherwise movable and apertured member or disc in order to create the higher than atmospheric pressure in the chamber. This forces seeds from a seed mass onto the seed member or disc where they are retained for later release. The apertures or holes in the rotating member or disc open to atmosphere where the individual seeds are held by the blowing air until the seeds are dispensed by interrupting the flow of air to the seeds.
While air seed meters of the positive pressure type offer certain advantages over mechanical seed meters, they have certain limitations of their own which may prove to be a significant disadvantage for various seeding applications. In an effort to fill each hole or opening with a seed as the seed disc rotates through the seed mass, a relatively high pressure differential is applied to the disc. Because the seeds are held in place on the rotating disc or other movable member by differential pressure resulting from positive pressure in the chamber, it is usually necessary that the air flow be directed through the seed mass to aid in the depositing of individual seeds onto the disc. The air flow has been found to interfere with the orderly delivery of seeds from the disc and, ultimately, to the ground. In positive pressure seed metering mechanisms, the seed hopper must be sealed to maintain pressure in the system. If for any reason the hopper lid comes off or the hopper otherwise becomes unsealed, the seed meter will not properly function.
Vacuum seed meters have been found to overcome some of the problems in the positive pressure seed meters and offer more control over the seed being transported by the seed disc. In vacuum seed meters, a vacuum source is typically coupled to a separate chamber on the opposite of the seed disc from the seed mass with the vacuum communicating through the apertures in the seed disc to the seed mass. The vacuum is of sufficient magnitude such that it tends to draw seeds into the openings defined by the disc and hold the seeds thereto as the seeds are moved through the seed disc under the influence of the moving seed disc toward the seed discharge area of the seed metering mechanism. The openings between the outer surface of the seeds and the periphery of the openings in the disc allows air to pass therethrough thereby maintaining the seeds in operable association with the disc. Because the pressure differential at the seed disc comes from a vacuum source on the opposite side thereof and not from the flow of air at the same side thereof as with positive pressure type seed metering mechanisms, the problem of having to direct an air flow through the seed mass and on to the seed disc are eliminated.
Despite the various advantages of vacuum seed meters over seed meters of the positive pressure type, presently known vacuum seed meters are not without problems of their own. For one thing, testing has revealed that when vacuum seed metering mechanisms are used some seeds tend to be drawn rotationally under the influence of the moving seed disc and the vacuum in the discharge area of the seed metering mechanism rather than gravitationally falling for deposit to the ground. Testing has also revealed that the air drawn through the openings between the outer surface of the seeds and the periphery of the openings in the seed disc in the seed discharge area of the seed metering mechanism tends to flow upwardly into the seed metering mechanism in a direction opposed to the direction the seeds are intended to flow under the influence of gravity. Moreover, some vacuum seed metering mechanisms include a seed disc having a pocket or recess arranged in radially extending relation relative to the opening for accommodating a seed therewithin. When the respective openings reach the seed discharge area whereat the vacuum to the seed disc is cutoff, the seeds carried in the pockets tend to move with the disc. The seeds entrapped within the pockets and moving rotationally with the disc, however, tend to interfere with other seeds being released from the disc in the seed discharge area thereby effecting accurate seed spacing between adjacent individual seeds.
Accordingly, it would be desirable to provide a seed planter which includes vacuum seed metering mechanism wherein the release of seeds from the disc is effected positively without seeds sticking or hanging onto the seed disc or releasing erratically therefrom as a result of the vacuum used in combination with the seed mechanism. Moreover, providing a seed disc with a low friction seed release advantageously eliminates or significantly reduces the tendency or likelihood of the seeds to be, carried with or rotationally move with the seed disc allows the seeds discharged from the seed metering disc to be readily and reliably released from the seed disc without the need for complicated release mechanisms.